1. Field of the Invention
The present invention relates to a process for preparing a curable polyphenylene ether (PPE) resin. More particularly, the present invention relates to a process for preparing a curable polyphenylene ether resin, which involves introducing an epoxy group-containing functional group to the terminal end of PPE (Mn greater than 3000) by modifying the hydroxy and ester groups on the terminal end.
2. Description of the Prior Art
Communication devices tend to function at higher speeds and frequencies. The substrate material for such devices, such as wireless communication networks, satellite communication equipment, high performance and broadband devices, high speed computers and computer work stations, demands a high glass transition temperature (Tg), low dielectric constant (Dk), and low loss factor (Df). Presently, the copper-clad laminate used for printed circuit boards (PCB) is mainly FR-4, the substrate of which is epoxy resin. However, electrical properties (such as Dk and Df) of FR-4 can no longer meet the increasing needs of high frequency.
Polyphenylene ether (PPE), having high Tg and superior electrical properties, is a potential material for high frequency substrates. Therefore, PPE resin has been introduced into the epoxy-made FR-4 substrate, in order to enhance the limited properties of epoxy resin. However, epoxy resin and PPE resin have great difference in chemical structure. Thus, the chemical comparability between these two resins is inferior. When epoxy and PPE resins are mixed, they cannot undergo crosslinking, and phase separation occurs. It is very difficult to use the PPE-Epoxy resin system in printed circuit boards. Therefore, some researchers have attempted to solve the phase separation when PPE and epoxy are mixed.
For example, in U.S. Pat. No. 4,853,423, after PPE and epoxy resins are mixed, zinc acetylacetonate or zinc stearate is added as a compatabilizer. Thus, coordination bonding is generated between PPE and epoxy and no phase separation occurs. However, the addition of these metal salts makes the substrate have inferior electrical properties.
In U.S. Pat. No. 5,834,565, PPE resin is modified to have a smaller molecular weight. The smaller the molecular weight of PPE, the less chance the phase separation between PPE and epoxy. However, when PPE has a too small molecular weight, particularly less than 3000, the PPE-epoxy resin has inferior electrical properties. The addition of PPE is in vain.
In Japanese Patent No. 09291148, PPE resin is redistributed to obtain a PPE resin with Mn of 1000 to 3000. Then, epoxy functional groups are introduced into the redistributed PPE. Although small-molecular-weight PPE resin has better processability, the glass transition temperature is adversely decreased.
Therefore, there is still a need to develop a new process to solve the inferior comparability and phase separation between PPE and epoxy and to obtain an epoxy group-containing PPE with high glass transition temperature.
An object of the present invention is to solve the above-mentioned problems and to provide a process for preparing an epoxy group-containing curable polyphenylene ether resin with high glass transition temperature.
To achieve the above objects, the process for preparing an epoxy group-containing curable polyphenylene ether (PPE) resin of the present invention includes reacting a polyphenylene ether resin represented by formula (I), a strong base, and a compound containing a leaving group and epoxy group to obtain a curable polyphenylene ether resin represented by formula (II).
Formula (I) has a number average molecular weight higher than 3000 and is 
wherein
R1 can be the same or different and is H, alkyl having from 1 to 3 carbon atoms, or 
xe2x80x83wherein R11 is alkylene having from 1 to 3 carbon atoms, and R12 is aryl;
Z1 can be the same or different and is H, OH, or 
xe2x80x83and at least one Z1 is OH or 
xe2x80x83wherein R13 is aryl; and
p is from 25 to 165.
The compound containing leaving group and epoxy group has the formula (A): 
wherein
X is a leaving group of halogen or sulfonate; and
n is an integer of 1 to 6.
Formula (II) is: 
wherein
R2 can be the same or different and is H, alkyl having from 1 to 3 carbon atoms, 
xe2x80x83wherein
R11 is alkylene having from 1 to 3 carbon atoms;
R12 is aryl;
n is an integer of 1 to 6; and
s is 0 or an integer of 1 to 6;
Z2 can be the same or different and is H, OH, 
xe2x80x83and at least one is a group represented by formula (i), wherein R13 is aryl, n and s are defined above; and
p is 25 to 165.